Positioning device and positioning method

1. A positioning device comprising: a signal receiver configured to receive a plurality of positioning signals respectively transmitted from a plurality of positioning satellites; an environment index value calculator configured to sequentially calculate, as an index value for determining whether in a multipath environment, at least one of a Doppler shift amount and a pseudo distance of each of the positioning satellites based on each of the positioning signals received by the signal receiver; a dispersion calculator configured to calculate an index value dispersion indicating a degree of variation of the index value calculated by the environment index value calculator for each of captured satellites which are the positioning satellites from which the positioning signals are received by the signal receiver; a primary selector configured to determine a non-use satellite not to be used in a positioning calculation processing among the captured satellites based on the index value dispersion calculated by the dispersion calculator for each of the captured satellites; an environment determiner configured to determine whether a surrounding environment is an environment in which a multipath is likely to occur based on a deletion rate which is a ratio of the number of the captured satellite set as the non-use satellite by the primary selector to a total number of the captured satellites; a condition changer configured to change a condition of the captured satellites to be used in the positioning calculation processing based on a determination result of the environment determiner; and a positioning calculator configured to perform the positioning calculation processing using the positioning signals from the positioning satellites that satisfy the condition set by the condition changer.

2. The positioning device according to claim 1 , wherein a plurality of categories is set in stages in advance according to a likelihood of occurrence of the multipath, the categories include at least an open sky category, which is a category corresponding to an open sky environment in which the multipath is least likely to occur, and an urban category, which is a category corresponding to an urban area in which the multipath is most likely to occur, the environment determiner determines which of the categories the surrounding environment corresponds to based on the deletion rate, and the condition changer is configured to set the condition of the captured satellites to be used in the positioning calculation processing to be stricter when the surrounding environment determined by the environment determiner corresponds to the category in which the multipath is less likely to occur.

3. The positioning device according to claim 2 , further comprising: an error index value calculator configured to calculate, for each primary remaining satellite which is the captured satellite not set as the non-use satellite by the primary selector, an error index value representing a magnitude of a possibility that a pseudo distance calculated based on the positioning signal transmitted from the captured satellite includes an error, wherein the condition of the captured satellite used in the positioning calculation processing is that the error index value is less than a filtering threshold set by the condition changer; and the condition changer is configured to set the filtering threshold to a smaller value in a state where the surrounding environment determined by the environment determiner corresponds to the category in which the multipath is less likely to occur.

4. The positioning device according to claim 3 , wherein the error index value is a pseudo distance residual representing a magnitude of a difference between a straight line distance from the positioning device to each of the captured satellites determined according to position coordinates of the positioning device and position coordinates of each of the captured satellites, and the pseudo distance of each of the captured satellites.

5. The positioning device according to claim 3 , wherein a plurality of candidate values is set in stages as the candidate values of the filtering threshold, the condition changer sets the filtering threshold to a smallest candidate value among the candidate values when the environment determiner determines that the surrounding environment corresponds to the open sky category, and the condition changer sets the filtering threshold to a largest candidate value among the candidate values when the environment determiner determines that the surrounding environment corresponds to the urban category.

6. The positioning device according to claim 3 , wherein a plurality of candidate values respectively associated with the categories is set as the candidate values of the filtering threshold, and the positioning satellites include at least one quasi-zenith satellite that orbits a quasi-zenith orbit for an area in which the positioning device is used, the positioning device further comprises a quasi-zenith capture determiner configured to determine whether the quasi-zenith satellite is captured based on an elevation angle of each of the captured satellites or transmission source information indicated in the positioning signal of each of the captured satellites, and the condition changer sets the filtering threshold to be the candidate value associated with the category determined by the environment determiner when the quasi-zenith capture determiner determines that the positioning signal from the quasi-zenith satellite is not captured, and sets the filtering threshold to be a value smaller than the candidate value associated with the category determined by the environment determiner when the quasi-zenith capture determiner determines that the positioning signal from the quasi-zenith satellite is captured.

7. The positioning device according to claim 2 , wherein a subject device as the positioning device is configured to be mutually communicably connected to a short range communicator for directly communicating with a peripheral device which is another positioning device existing within a predetermined distance from the subject device, the environment determiner is configured to broadcast category information indicating the category determined by the environment determiner of the subject device based on the deletion rate to the peripheral device in cooperation with the short range communicator, and the positioning device further comprises a majority determiner that acquires the category of the surrounding environment determined by the peripheral device in cooperation with the short range communicator and finally determines which of the categories the surrounding environment corresponds to according to a majority decision using determination results of the peripheral device and the subject device.

8. The positioning device according to claim 7 , wherein when a number of appearances of a most frequent category, which is the determination result having a largest number of appearances among the determination results of the peripheral device and the subject device, exceeds half of a total, the majority determiner determines that the surrounding environment corresponds to the most frequent category, and when the number of appearances of the most frequent category does not exceeds half of the total, the majority determiner employs the determination result of the subject device as a final surrounding environment.

9. The positioning device according to claim 1 , wherein part or all of the signal receiver, the environment index value calculator, the dispersion calculator, the primary selector, the environment determiner, the condition changer, and the positioning calculator are realized by software executed by a processor, or hardware, or cooperation of the software and the hardware.

10. A positioning device comprising a processor and a memory, the memory storing instructions configured to, when executed by the processor, cause the processor to: receive a plurality of positioning signals respectively transmitted from a plurality of positioning satellites; sequentially calculate, as an index value for determining whether in a multipath environment, at least one of a Doppler shift amount and a pseudo distance of each of the positioning satellites based on each of the positioning signals that are received; calculate an index value dispersion indicating a degree of variation of the index value calculated for each of captured satellites which are the positioning satellites from which the positioning signals are received; determine a non-use satellite not to be used in a positioning calculation processing among the captured satellites based on the index value dispersion calculated for each of the captured satellites; determine whether a surrounding environment is an environment in which a multipath is likely to occur based on a deletion rate which is a ratio of the number of the captured satellite set as the non-use satellite to a total number of the captured satellites; change a condition of the captured satellites to be used in the positioning calculation processing based on a determination result of the surrounding environment; and perform the positioning calculation processing using the positioning signals from the positioning satellites that satisfy the condition.

11. A positioning method comprising: receiving a plurality of positioning signals respectively transmitted from a plurality of positioning satellites; sequentially calculating, as an index value for determining whether in a multipath environment, at least one of a Doppler shift amount and a pseudo distance of each of the positioning satellites based on each of the positioning signals that are received; calculating an index value dispersion indicating a degree of variation of the index value calculated for each of captured satellites which are the positioning satellites from which the positioning signals are received; determining a non-use satellite not to be used in a positioning calculation processing among the captured satellites based on the index value dispersion calculated for each of the captured satellites; determining whether a surrounding environment is an environment in which a multipath is likely to occur based on a deletion rate which is a ratio of the number of the captured satellite set as the non-use satellite to a total number of the captured satellites; changing a condition of the captured satellites to be used in the positioning calculation processing based on a determination result of the surrounding environment; and performing the positioning calculation processing using the positioning signals from the positioning satellites that satisfy the condition.